wmadec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

                    if (a)
                        nb_coefs[ch] -= s->exponent_high_bands[bsize][i];
                }
            }
        }
        for(ch = 0; ch < s->nb_channels; ch++) {
            if (s->channel_coded[ch]) {
                int i, n, val, code;

                n = s->exponent_high_sizes[bsize];
                val = (int)0x80000000;
                for(i=0;i<n;i++) {
                    if (s->high_band_coded[ch][i]) {
                        if (val == (int)0x80000000) {
                            val = get_bits(&s->gb, 7) - 19;
                        } else {
                            code = get_vlc2(&s->gb, s->hgain_vlc.table, HGAINVLCBITS, HGAINMAX);
                            if (code < 0)
                                return -1;
                            val += code - 18;
                        }
                        s->high_band_values[ch][i] = val;
                    }
                }
            }
        }
    }

    /* exponents can be reused in short blocks. */
    if ((s->block_len_bits == s->frame_len_bits) ||
        get_bits1(&s->gb)) {
        for(ch = 0; ch < s->nb_channels; ch++) {
            if (s->channel_coded[ch]) {
                if (s->use_exp_vlc) {
                    if (decode_exp_vlc(s, ch) < 0)
                        return -1;
                } else {
                    decode_exp_lsp(s, ch);
                }
                s->exponents_bsize[ch] = bsize;
            }
        }
    }

    /* parse spectral coefficients : just RLE encoding */
    for(ch = 0; ch < s->nb_channels; ch++) {
        if (s->channel_coded[ch]) {
            VLC *coef_vlc;
            int level, run, sign, tindex;
            int16_t *ptr, *eptr;
            const uint16_t *level_table, *run_table;

            /* special VLC tables are used for ms stereo because
               there is potentially less energy there */
            tindex = (ch == 1 && s->ms_stereo);
            coef_vlc = &s->coef_vlc[tindex];
            run_table = s->run_table[tindex];
            level_table = s->level_table[tindex];
            /* XXX: optimize */
            ptr = &s->coefs1[ch][0];
            eptr = ptr + nb_coefs[ch];
            memset(ptr, 0, s->block_len * sizeof(int16_t));
            for(;;) {
                code = get_vlc2(&s->gb, coef_vlc->table, VLCBITS, VLCMAX);
                if (code < 0)
                    return -1;
                if (code == 1) {
                    /* EOB */
                    break;
                } else if (code == 0) {
                    /* escape */
                    level = get_bits(&s->gb, coef_nb_bits);
                    /* NOTE: this is rather suboptimal. reading
                       block_len_bits would be better */
                    run = get_bits(&s->gb, s->frame_len_bits);
                } else {
                    /* normal code */
                    run = run_table[code];
                    level = level_table[code];
                }
                sign = get_bits1(&s->gb);
                if (!sign)
                    level = -level;
                ptr += run;
                if (ptr >= eptr)
                {
                    av_log(NULL, AV_LOG_ERROR, "overflow in spectral RLE, ignoring\n");
                    break;
                }
                *ptr++ = level;
                /* NOTE: EOB can be omitted */
                if (ptr >= eptr)
                    break;
            }
        }
        if (s->version == 1 && s->nb_channels >= 2) {
            align_get_bits(&s->gb);
        }
    }

    /* normalize */
    {
        int n4 = s->block_len / 2;
        mdct_norm = 1.0 / (float)n4;
        if (s->version == 1) {
            mdct_norm *= sqrt(n4);
        }
    }

    /* finally compute the MDCT coefficients */
    for(ch = 0; ch < s->nb_channels; ch++) {
        if (s->channel_coded[ch]) {
            int16_t *coefs1;
            float *coefs, *exponents, mult, mult1, noise;
            int i, j, n, n1, last_high_band, esize;
            float exp_power[HIGH_BAND_MAX_SIZE];

            coefs1 = s->coefs1[ch];
            exponents = s->exponents[ch];
            esize = s->exponents_bsize[ch];
            mult = pow(10, total_gain * 0.05) / s->max_exponent[ch];
            mult *= mdct_norm;
            coefs = s->coefs[ch];
            if (s->use_noise_coding) {
                mult1 = mult;
                /* very low freqs : noise */
                for(i = 0;i < s->coefs_start; i++) {
                    *coefs++ = s->noise_table[s->noise_index] *
                      exponents[i<<bsize>>esize] * mult1;
                    s->noise_index = (s->noise_index + 1) & (NOISE_TAB_SIZE - 1);
                }

                n1 = s->exponent_high_sizes[bsize];

                /* compute power of high bands */
                exponents = s->exponents[ch] +
                    (s->high_band_start[bsize]<<bsize);
                last_high_band = 0; /* avoid warning */
                for(j=0;j<n1;j++) {
                    n = s->exponent_high_bands[s->frame_len_bits -
                                              s->block_len_bits][j];
                    if (s->high_band_coded[ch][j]) {
                        float e2, v;
                        e2 = 0;
                        for(i = 0;i < n; i++) {
                            v = exponents[i<<bsize>>esize];
                            e2 += v * v;
                        }
                        exp_power[j] = e2 / n;
                        last_high_band = j;
                        tprintf(s->avctx, "%d: power=%f (%d)\n", j, exp_power[j], n);
                    }
                    exponents += n<<bsize;
                }

                /* main freqs and high freqs */
                exponents = s->exponents[ch] + (s->coefs_start<<bsize);
                for(j=-1;j<n1;j++) {
                    if (j < 0) {
                        n = s->high_band_start[bsize] -
                            s->coefs_start;
                    } else {
                        n = s->exponent_high_bands[s->frame_len_bits -
                                                  s->block_len_bits][j];
                    }
                    if (j >= 0 && s->high_band_coded[ch][j]) {
                        /* use noise with specified power */
                        mult1 = sqrt(exp_power[j] / exp_power[last_high_band]);
                        /* XXX: use a table */
                        mult1 = mult1 * pow(10, s->high_band_values[ch][j] * 0.05);
                        mult1 = mult1 / (s->max_exponent[ch] * s->noise_mult);
                        mult1 *= mdct_norm;
                        for(i = 0;i < n; i++) {
                            noise = s->noise_table[s->noise_index];
                            s->noise_index = (s->noise_index + 1) & (NOISE_TAB_SIZE - 1);
                            *coefs++ =  noise *
                                exponents[i<<bsize>>esize] * mult1;
                        }
                        exponents += n<<bsize;
                    } else {
                        /* coded values + small noise */
                        for(i = 0;i < n; i++) {
                            noise = s->noise_table[s->noise_index];
                            s->noise_index = (s->noise_index + 1) & (NOISE_TAB_SIZE - 1);
                            *coefs++ = ((*coefs1++) + noise) *
                                exponents[i<<bsize>>esize] * mult;
                        }
                        exponents += n<<bsize;
                    }
                }

                /* very high freqs : noise */
                n = s->block_len - s->coefs_end[bsize];
                mult1 = mult * exponents[((-1<<bsize))>>esize];
                for(i = 0; i < n; i++) {
                    *coefs++ = s->noise_table[s->noise_index] * mult1;
                    s->noise_index = (s->noise_index + 1) & (NOISE_TAB_SIZE - 1);
                }
            } else {
                /* XXX: optimize more */
                for(i = 0;i < s->coefs_start; i++)
                    *coefs++ = 0.0;
                n = nb_coefs[ch];
                for(i = 0;i < n; i++) {
                    *coefs++ = coefs1[i] * exponents[i<<bsize>>esize] * mult;
                }
                n = s->block_len - s->coefs_end[bsize];
                for(i = 0;i < n; i++)
                    *coefs++ = 0.0;
            }
        }
    }

#ifdef TRACE
    for(ch = 0; ch < s->nb_channels; ch++) {
        if (s->channel_coded[ch]) {
            dump_floats(s, "exponents", 3, s->exponents[ch], s->block_len);
            dump_floats(s, "coefs", 1, s->coefs[ch], s->block_len);
        }
    }
#endif

    if (s->ms_stereo && s->channel_coded[1]) {
        float a, b;
        int i;

        /* nominal case for ms stereo: we do it before mdct */
        /* no need to optimize this case because it should almost
           never happen */
        if (!s->channel_coded[0]) {
            tprintf(s->avctx, "rare ms-stereo case happened\n");
            memset(s->coefs[0], 0, sizeof(float) * s->block_len);
            s->channel_coded[0] = 1;
        }

        for(i = 0; i < s->block_len; i++) {
            a = s->coefs[0][i];
            b = s->coefs[1][i];
            s->coefs[0][i] = a + b;
            s->coefs[1][i] = a - b;
        }
    }

    for(ch = 0; ch < s->nb_channels; ch++) {
        if (s->channel_coded[ch]) {
            int n4, index, n;

            n = s->block_len;
            n4 = s->block_len / 2;
            s->mdct_ctx[bsize].fft.imdct_calc(&s->mdct_ctx[bsize],
                          s->output, s->coefs[ch], s->mdct_tmp);

            /* multiply by the window and add in the frame */
            index = (s->frame_len / 2) + s->block_pos - n4;
            wma_window(s, &s->frame_out[ch][index]);

            /* specific fast case for ms-stereo : add to second
               channel if it is not coded */
            if (s->ms_stereo && !s->channel_coded[1]) {
                wma_window(s, &s->frame_out[1][index]);
            }
        }
    }
 next:
    /* update block number */
    s->block_num++;
    s->block_pos += s->block_len;
    if (s->block_pos >= s->frame_len)
        return 1;
    else
        return 0;
}

/* decode a frame of frame_len samples */
static int wma_decode_frame(WMACodecContext *s, int16_t *samples)
{
    int ret, i, n, ch, incr;
    int16_t *ptr;
    float *iptr;

#ifdef TRACE
    tprintf(s->avctx, "***decode_frame: %d size=%d\n", s->frame_count++, s->frame_len);
#endif

    /* read each block */
    s->block_num = 0;
    s->block_pos = 0;
    for(;;) {
        ret = wma_decode_block(s);
        if (ret < 0)
            return -1;
        if (ret)
            break;
    }

    /* convert frame to integer */
    n = s->frame_len;
    incr = s->nb_channels;
    for(ch = 0; ch < s->nb_channels; ch++) {
        ptr = samples + ch;
        iptr = s->frame_out[ch];

        for(i=0;i<n;i++) {
            *ptr = av_clip_int16(lrintf(*iptr++));
            ptr += incr;
        }
        /* prepare for next block */
        memmove(&s->frame_out[ch][0], &s->frame_out[ch][s->frame_len],
                s->frame_len * sizeof(float));
    }

#ifdef TRACE
    dump_shorts(s, "samples", samples, n * s->nb_channels);
#endif
    return 0;
}

static int wma_decode_superframe(AVCodecContext *avctx,
                                 void *data, int *data_size,
                                 uint8_t *buf, int buf_size)
{
    WMACodecContext *s = avctx->priv_data;
    int nb_frames, bit_offset, i, pos, len;
    uint8_t *q;
    int16_t *samples;

    tprintf(avctx, "***decode_superframe:\n");

    if(buf_size==0){
        s->last_superframe_len = 0;
        return 0;
    }

    samples = data;

    init_get_bits(&s->gb, buf, buf_size*8);

    if (s->use_bit_reservoir) {
        /* read super frame header */
        skip_bits(&s->gb, 4); /* super frame index */
        nb_frames = get_bits(&s->gb, 4) - 1;

        bit_offset = get_bits(&s->gb, s->byte_offset_bits + 3);

        if (s->last_superframe_len > 0) {
            //        printf("skip=%d\n", s->last_bitoffset);
            /* add bit_offset bits to last frame */
            if ((s->last_superframe_len + ((bit_offset + 7) >> 3)) >
                MAX_CODED_SUPERFRAME_SIZE)
                goto fail;
            q = s->last_superframe + s->last_superframe_len;
            len = bit_offset;
            while (len > 7) {
                *q++ = (get_bits)(&s->gb, 8);
                len -= 8;
            }
            if (len > 0) {
                *q++ = (get_bits)(&s->gb, len) << (8 - len);
            }

            /* XXX: bit_offset bits into last frame */
            init_get_bits(&s->gb, s->last_superframe, MAX_CODED_SUPERFRAME_SIZE*8);
            /* skip unused bits */
            if (s->last_bitoffset > 0)
                skip_bits(&s->gb, s->last_bitoffset);
            /* this frame is stored in the last superframe and in the
               current one */
            if (wma_decode_frame(s, samples) < 0)
                goto fail;
            samples += s->nb_channels * s->frame_len;
        }

        /* read each frame starting from bit_offset */
        pos = bit_offset + 4 + 4 + s->byte_offset_bits + 3;
        init_get_bits(&s->gb, buf + (pos >> 3), (MAX_CODED_SUPERFRAME_SIZE - (pos >> 3))*8);
        len = pos & 7;
        if (len > 0)
            skip_bits(&s->gb, len);

        s->reset_block_lengths = 1;
        for(i=0;i<nb_frames;i++) {
            if (wma_decode_frame(s, samples) < 0)
                goto fail;
            samples += s->nb_channels * s->frame_len;
        }

        /* we copy the end of the frame in the last frame buffer */
        pos = get_bits_count(&s->gb) + ((bit_offset + 4 + 4 + s->byte_offset_bits + 3) & ~7);
        s->last_bitoffset = pos & 7;
        pos >>= 3;
        len = buf_size - pos;
        if (len > MAX_CODED_SUPERFRAME_SIZE || len < 0) {
            goto fail;
        }
        s->last_superframe_len = len;
        memcpy(s->last_superframe, buf + pos, len);
    } else {
        /* single frame decode */
        if (wma_decode_frame(s, samples) < 0)
            goto fail;
        samples += s->nb_channels * s->frame_len;
    }

//av_log(NULL, AV_LOG_ERROR, "%d %d %d %d outbytes:%d eaten:%d\n", s->frame_len_bits, s->block_len_bits, s->frame_len, s->block_len,        (int8_t *)samples - (int8_t *)data, s->block_align);

    *data_size = (int8_t *)samples - (int8_t *)data;
    return s->block_align;
 fail:
    /* when error, we reset the bit reservoir */
    s->last_superframe_len = 0;
    return -1;
}

AVCodec wmav1_decoder =
{
    "wmav1",
    CODEC_TYPE_AUDIO,
    CODEC_ID_WMAV1,
    sizeof(WMACodecContext),
    wma_decode_init,
    NULL,
    ff_wma_end,
    wma_decode_superframe,
};

AVCodec wmav2_decoder =
{
    "wmav2",
    CODEC_TYPE_AUDIO,
    CODEC_ID_WMAV2,
    sizeof(WMACodecContext),
    wma_decode_init,
    NULL,
    ff_wma_end,
    wma_decode_superframe,
};